"She said yes!!!" Derek tweeted along with the photo.
Derek also shared a clip of Saffron showing off her engagement ring on his Instagram Stories, according toPeople.
Derek revealed Wednesday on Instagram that Saffron's ring is comprised of a custom-made emerald-cut diamond. He apparently asked one of her jeweler friends to help him design the ring.
Saffron began sharing funny moments from her relationship with Derek through TikTok videos in March, Us Weekly reported, and Derek posted some cute clips of his own in May while the couple was quarantining together amid the ongoing coronavirus pandemic.
Before Derek became romantically involved with Saffron, who has modeled on the covers of Vogue India and British Vogue, he told Us that he was actually considering appearing on Bachelor in Paradise for the third time -- but ultimately chose not to do another stint.
"I'm not making an official statement, but right now, I don't see me doing another show," Derek told the magazine in September 2019. "Then again, I think I said that last time. I'm not sure."
Bachelor in Paradise's seventh season, however, never filmed due to Clare Crawley's season of The Bachelorette being postponed for about four months due to COVID-19.
Since The Bachelorette began filming in the middle of July and The Bachelor's currently-filming 25th season starring Matt James will premiere on ABC in January, this year's edition of Bachelor in Paradise was scrapped altogether.
Derek found fame when he competed for JoJo Fletcher's heart on Season 12 of The Bachelorette.
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When his relationship with JoJo didn't work out, Derek went on to find love on Bachelor in Paradise's fourth season in 2017 with Taylor Nolan, whom he got engaged to during the finale.
Taylor and Derek, however, announced their decision to split and call off their engagement in late June 2018 after trying to make a long-distant relationship work.
"We put everything we could into our relationship and are heartbroken to go forward separately, but we know this is the best decision for the both of us," the pair told Us in a joint statement at the time.
Derek subsequently appeared on Bachelor in Paradise's sixth season last summer and became a fan-favorite.
While Season 6 of BIP was airing in August 2019, Derek landed a lot of support to become the franchise's leading man for 2020, before Peter Weber was officially announced as The Bachelor star for Season 24.
Derek fell hard for Demi in Paradise and they quickly became the most established and healthy couple in Mexico, but Demi was secretly thinking about a woman she had been dating at home prior to the show, Kristian Haggerty.
The more Demi got to know and care for Derek, the more she thought about and missed Kristian as well. Demi therefore had to be open with Derek about where she stood, and he was nothing but compassionate and supportive.
"I can't put myself in her shoes. Truth be told, I can't understand the level of bravery and courage that it took to say to me," Derek told the cameras.
Derek hoped to continue his relationship with Demi despite the fact she had strong feelings for someone else, but she ultimately chose Kristian and Derek got hurt.
Derek vented at the time about how he's never a woman's first choice. He was tired of being told he's "a great" or "amazing" guy considering he never seemed to end up with the girl.
Derek later quitBachelor in Paradise after having a brief fling with Tayshia Adams, who is currently starring on The Bachelorette's sixteenth season, that ended with her dumping him as well.