Photo: Instagram

Cody Simpson has marked his six-month anniversary with Miley Cyrus, by expressing his love for her in a heartfelt dedication.

The singer made the public declaration on his Instagram Story on Wednesday, insisting their brief romance feels like it has lasted "a lifetime."

"Six months with you is worth a lifetime with anyone else. I love you," he captioned a shot of the couple together.

The two stars sparked rumours they were dating after they were spotted out and about together in Los Angeles last October.

The Wrecking Ball hitmaker and Simpson, who will join Miley on her daily Instagram Live show Bright Minded on Thursday, recently adopted a German Shepherd puppy, named Bo, together.