The Formula 1 racing driver and the singer - who celebrated their fifth anniversary last month - look set to tie the knot after Lewis subtly suggested he may pop the question to the brunette beauty before their budding relationship enters into its sixth year.
He is quoted by The Sun newspaper as saying: ''We've been together for five years, which is quite a milestone really.
''But hopefully [I'll propose] in the near future before we get to six years.''
The 'Boomerang' singer - who battled with an eating disorder during her time in chart-topping girl band, the Pussycat Dolls - has revealed that the British-born racer's encouragement finally made her feel comfortable in her own skin.
She said previously: ''He made me feel beautiful for who I am not what pant size I'm wearing, and that helped a lot. I started to embrace myself as a woman and my curves.''
Nicole admitted last year that the pair - who briefly split in 2010 - are a perfect match for each other because they've both been brought up the same way.
She said: ''Me and Lewis are from similar upbringings so we share a similar outlook. We're kindred spirits and hearts - that's what ultimately connects us.''