FatalErrorException in Model.php line 750: Class not found Laravel5

I'm currently in the process of upgrading a Laravel 4.2 project to 5.0 I've been making reasonable progress until this particular error:

FatalErrorException in Model.php line 750: Class 'SAPProduct' not found.

My SapProduct class is called from my Product class with a hasOne relationship and I can't work out why Laravel can't find it.

SapProduct.php

namespace App\Models;

use Eloquent;

class SapProduct extends Eloquent
{
    public function brand()
    {
        return $this->belongsTo('App\Models\Brand', 'U_Brand', 'Name');
    }
}

Product.php

namespace App\Models;

use Eloquent;

class Product extends Eloquent
{
    ...
    public function sapProduct()
    {
        $relationship = $this->hasOne('App\Models\SapProduct', 'ItemCode', 'itemcode');
    }
    ...
}

Model.php (lines 746-755)

public function hasOne($related, $foreignKey = null, $localKey = null)
{
    $foreignKey = $foreignKey ?: $this->getForeignKey();

    $instance = new $related;

    $localKey = $localKey ?: $this->getKeyName();

    return new HasOne($instance->newQuery(), $this, $instance->getTable().'.'.$foreignKey, $localKey);
}

I apologise if I'm missing any other necessary information, I'll add more as/if requested.

Thanks

via Chebli Mohamed