Lee, who is one third of boy band 911, is now dating celebrity make-up artist Lila Rose Holliday after meeting her on last year's series of The Big Reunion.
Lila is also an aspiring singer and Lee has now tweeted a link to a YouTube video which shows her belting out Ariana Grande and Nathan Sykes' duet 'Almost Is Never Enough' in her kitchen.
Lee told his followers: "Have a listen to my gf Lila, amazing voice!"
The star's fans were quick to respond, and among the messages of praise was one from his estranged wife Lindsay - who also reformed with her band B*Witched for last year's Big Reunion.
She simply commented: "@MrLeeBrennan @MUA_LilaRose Amazing!!" Lila then replied with several flower icons, saying: "Thank you."
In February 2013, Lee held back tears as he spoke about his split with Lindsay on The Big Reunion.
The couple had been married since 2006 and had separated the previous year but, if anything, being brought back together for the ITV2 show helped Lee move on.
In an interview with Reveal seven months later, Lee admitted: "I didn't realise how much I would [wear my heart on my sleeve].
"I was just being truthful about how I felt about somebody and I guess that's helped a bit with moving on."
Watch Lee's video of Lila here: